Examples of electronic components include crystal resonators, crystal filters, crystal oscillators, and other such piezoelectric resonator devices. With these piezoelectric resonator devices, a metal thin film electrode is formed on the surface of a crystal resonator plate (piezoelectric resonator plate) as an electronic component element, and this crystal resonator plate is hermetically sealed into a package (an electronic component package formed by a metal base being resistance welded to a metal cap) in order to protect the metal thin film electrode from the outside atmosphere. These crystal resonators are widely used as sources of reference for frequency and time because of their outstanding resonance characteristics.
The package shown in FIG. 11 (a cross-sectional view illustrating a conventional example) and FIG. 12 (an enlarged cross-sectional view of a welded portion in FIG. 11) is an example of a conventional electronic component package in which a metal base and a metal cap are joined by resistance welding to hermetically seal an electronic component element. As shown in FIGS. 11 and 12, with this conventional package, a flange 913 is formed on a metal base 91, and a triangular protrusion 914 is formed on this flange 913.
As shown in FIG. 11, this package includes slender, cylindrical metal lead terminals 911 and 912 that are erected passing through the package via insulating glass (not shown). A metal cap 92 includes an element compartment 915 and a flange 921. The metal base 91 or the metal cap 92 is plated with nickel or another such metal (not shown). A crystal resonator plate 93, which is an electronic component element, is mounted on the metal base 91, the crystal resonator plate 93 is covered with the metal cap 92, and power is electrically turned on in a state in which the protrusion 914 on the flange 913 of the metal base 91 has been press-bonded to the flange 921 of the metal cap 92, which melts the protrusion 914 and the metal plating and joins the metal base 91 and the metal cap 92 by resistance welding. The welding current is locally concentrated in the protrusion 914 during resistance welding, and this raises welding efficiency.
With a configuration such as this, however, in the resistance welding of the metal base 91 and the metal cap 92, the flange 921 of the metal cap 92 comes into contact with the protrusion 914, and this contact can crush the protrusion 914 or cause the metal plating to peel off. Also, when the protrusion 914 comes into contact with the flange 921, metal microparticles may be scattered, which is known as splash. These scattered metal microparticles often find their way inside the metal base 91, and if the electronic component is a crystal resonator or the like, the metal microparticles will adhere to the electrode surfaces of the electronic component element (the crystal resonator plate 93), causing electrode shorting, capacity fluctuation, and other such adverse effects to the characteristics.
In view of this, one of the ways proposed in the past for dealing with such problems, as disclosed in Patent Document 1, for example, is to have the apex of the protrusion located no more than 25% from the outer end of the flange of the metal base with respect to the total width of the flange. More specifically, the cross sectional shape of the protrusion is made to be a substantially right triangle with a gentle slope on the inside and the outer side cut off, and this reduces splash from getting into the interior.
Patent document 1: JP H6-9226U